1. Field of the Invention
The invention relates to a dental instrument with an instrument part and a handle part.
2. Description of Related Art
Dental instruments, especially root canal preparation instruments, arc subjected during use by the dentist to compressive, tensile, torsional and bending stresses with changing cycles, changing directions of rotation and with simultaneous movement up and down, i.e. when moved in the axial direction. Moreover, dental instruments are exposed to stresses of a chemical type from disinfectants and thermal stresses during hot sterilization. These stresses to which dental instruments are exposed leave traces on the used instruments, for example, deformation, twists by over-turning, and so forth.
As result of the effects of such stresses, these instruments must be disposed of after being used only three to five times, since there is the danger that they will break if they continue to be used. To do this, it is advantageous if the dentist is able to recognize on the dental instrument how many times it has already been used and sterilized.
For a root canal preparation instrument, it is disclosed in published German Patent Application DE 4 413 804 A1 to provide a movable element on the handle part which can be moved into several discrete positions. The dentist can move the movable element after each use by one of the discrete positions and read the number of times it has been used from the respective position.
This known approach is admittedly well suited for the indicated purpose, but has the defect that it cannot be precluded that the movable element will be unintentionally moved when the instrument is being used or sterilized, so that the number of times it has been used which can be read on the respective position of the movable element is incorrect.